(1) Field of Invention
The present invention generally relates to ignition systems for an internal combustion engine, and more particularly to an ignition system for an internal combustion engine which carries out a fuel cut control.
(2) Description of Related Art
As is well known, a conventional fuel injection control for an internal combustion engine employs a control such that a fuel cut is carried out when the internal combustion engine is working under a predetermined condition. An automotive vehicle equipped with a traction control system (frequently referred to as a TRC system) is known. The traction control system suppresses a wheel spin caused by, for example, an excessive driving force when the vehicle starts to move and accelerate on a snow-covered road, in order to ensure the stability of a vehicle traveling direction and appropriate vehicle driving force. The traction control system can be realized by various methods. For example, a fuel cut control directed to reducing the engine output power to suppress the wheel spin (see Japanese Laid-Open Patent Application No. 62-170754 and No. 60-104730).
An internal combustion engine employing such a fuel cut control has a problem in that if the fuel cut is terminated at an inadequate restoration timing, the combustion and expansion stroke will start under the condition where an appropriate amount of fuel for combustion has not yet been sucked into a cylinder or cylinders of the engine. For example, an internal combustion engine designed to have a necessary amount of fuel by injecting fuel twice has the following problem. If the first fuel injection is carried out during the time the fuel cut control is being carried out and the second fuel injection is carried out after the fuel cut control is terminated, the combustion and expansion stroke will start in a state where a cylinder has the fuel injected during only the second fuel injection. In this case, the combustion and expansion stroke is performed where a combustion room has an amount of fuel half the amount of fuel necessary for combustion. That is, the combustion and expansion stroke is carried out for a lean air-fuel ratio mixture.
When the air-fuel mixture is lean, it takes a long time to burn the air-fuel mixture and a live charcoal remains in the next suction (intake) stroke. In this case, the air-fuel mixture burns in the next suction stroke, so that back-fire occurs and drivability deteriorates greatly.